The present invention relates in general to automotive audio systems, and, more specifically, to an audio system interacting with a vehicle suspension system for controlling audio reproduction level in response to rough road conditions.
In-vehicle entertainment systems reproduce audio programs from sources such as an AM/FM tuner, CD or cassette player, or a DVD or video tape player. A volume control is provided for manually adjusting amplifier gain so that the reproduced audio generated by loudspeakers has a desired sound pressure level. When a vehicle is moving, fluctuating levels of background sound are created which interfere with the ability of the vehicle occupants to hear the audio program. During times of significant background sound levels, it may become desirable to boost the volume of the audio playback to maintain consistent audibility of the audio program for the listeners.
Audio systems are known which measure an ambient noise level in the vehicle passenger cabin for the purpose of generating an audio boost proportional to the ambient noise. These systems, however, are relatively expensive. A microphone or other transducer to measure the ambient sound and a dedicated microphone signal input to the audio system are required, which results in increased component and manufacturing costs. Since the sound picked up by the microphone includes both the background sound and the audio program signal being reproduced by the audio system, the audio program signal must be subtracted from the microphone signal before the background sound level is determined. This results in complex signal processing and further increases the component costs.
Costs associated with the microphone have been avoided by controlling audio gain in response to an inference of the magnitude of interfering noise sources based on the vehicle's speed of movement. As vehicle speed increases, engine noise and wind noise typically increase. Thus, various schemes for increasing audio volume using vehicle speed as measured by a vehicle speedometer have been tried. These systems are not completely effective because the interfering noise level can vary greatly while traveling at the same speed. For example, a vehicle traveling on smooth pavement may be subject to less road induced noise than one traveling on a bumpy roadway. Wind noise depends not only on the vehicle speed, but also on the direction and speed of the ambient wind. Thus, there is no consistent relationship between vehicle speed and the magnitude of background noise.